how to initialize a non copyable object data member

Question

I want to use an already implemented abstract class (which can be seen as "A" in my simple provided code) in my code. I defined class "B" to implement those pure virtual methods. The fact, here, is that the objects of this class cannot be copyable then, as the operator= is deleted in abstract class. I have class "Z" which has a data member of "B" class object. I want to initialize the object as you see in the code. But as it is a non-copyable one, for sure it show errors like use of deleted function ‘NS::B::B(NS::B&&)’ . I don't know how should I have this object as data member and also initialize it with proper data. The simple version of the code is as follow:

#include <string>
#include <iostream>
#include <memory>

namespace NS {
class A //abstract class
{
public:
    A() = default;
    A& operator=(const A& other) = delete;
    A(const A& other) = delete;
};
}

namespace NS {
class B : public A
{
public:
    B(int p);
};
}

namespace SI {
class Z
{
public:
    Z(int p, std::string name);
private:
    NS::B obj3;
};
typedef std::shared_ptr<SI::Z> ZPtr;
}

SI::Z::Z(int p, std::string name) : obj3(p)
{}

namespace SI {
class Y
{
public:
    Y(int p);
private:
    SI::ZPtr obj2;
};
}

SI::Y::Y(int p) : obj2(std::make_shared<SI::Z>(SI::Z(p,"hi")))
{}

probably just missing includes, but I get loads of errros that are unrelated to your question: https://wandbox.org/permlink/umVfs33yaFnIaLON — 463035818_is_not_an_ai, Apr 03 '19 at 16:15
you know that `class A : B` is private inheritance, right? for inheriting the interface private inheritance makes not much sense... — 463035818_is_not_an_ai, Apr 03 '19 at 16:16
user463035818 Sorry, I forgot to copy the includes. now I edited that. and also it should be copiled with c++11. I also corrected public inheritance, although it isnot affected on the problem. — Adroit, Apr 03 '19 at 16:19
You CAN initialize your object. You CAN'T use std::make_shared. — KonstantinL, Apr 03 '19 at 16:24

score 2 · Accepted Answer · answered Apr 03 '19 at 16:25

To make the above compile:

Add the headers:

#include <string>
#include <memory>

You also need to be able to construct the A so you need to make the constructors public:

class A //abstract class
{
    public:               // Added this:
         A() = default;
    .....
};

Your main issue is here in making the shared object.

 obj2(std::make_shared<SI::Z>(SI::Z(p,"hi")))

You don't need to constructed the SI::Z object here (as it is not copyable this is an issue). What you want to do is pass the arguments that will be used to create the SI::Z object. Then std::make_shared() will call new and forward these parameters to the constructor.

 obj2(std::make_shared<SI::Z>(p, "hi"))     // Notice the diff?

how to initialize a non copyable object data member

1 Answers1